A new analysis suggests that about 3.4 million Americans age 71 and
older—one in seven people in that age group—have dementia, and 2.4
million of them have Alzheimer’s disease (AD). The study, supported by
the National Institutes of Health (NIH), is the latest in a series of
analyses attempting to assess the prevalence of dementia and AD, the
most common form of dementia. Published online this week in Neuroepidemiology,
the study is the first to estimate rates of dementia and AD using a
nationally representative sample of older adults across the United
States. Brenda L. Plassman, Ph.D., of Duke University Medical Center, with
Kenneth M. Langa, M.D., Ph.D., and David R. Weir, Ph.D., of the
University of Michigan, Robert B. Wallace, Ph.D., of the University of
Iowa, and others, conducted the analysis as part of the Aging,
Demographics and Memory Study (ADAMS). ADAMS is a sub-study of the
larger Health and Retirement Study (HRS), the leading resource for data
on the combined health and economic circumstances of Americans over age
50. ADAMS and the HRS are sponsored by the National Institute on Aging
(NIA), a component of NIH, under a cooperative agreement with the
University of Michigan. The study highlights the nationwide reach of dementia, which affects
not only those with the disease, but their families and communities as
well. “As the population ages during the next few decades, the
prevalence of Alzheimer’s disease will increase several-fold unless
effective interventions are discovered and implemented,” said NIA
Director Richard J. Hodes, M.D. “These data underscore the urgency of
research in this area.” The study included 856 HRS participants age 71 and older from 42
states in 2001-2003. ADAMS interviewers from Duke University Medical
School conducted at-home evaluations to gather information about each
participant’s cognitive and functional status and symptoms,
neuropsychiatric symptoms, current medications, medical history and
family history of memory problems. Prior neuroimaging and laboratory
results were also obtained. A team of clinicians reviewed the evaluation information and made a
preliminary assessment of each person’s cognitive status. A consensus
panel of other medical experts then used well-accepted diagnostic
criteria to determine if the participant had normal cognitive function,
cognitive impairment without dementia, or dementia. Such criteria
further were used to discern the type of dementia, including AD or
vascular dementia, the second most common cause of dementia in older
adults. Based on the experts’ classifications, Drs. Plassman and Langa and
co-authors estimated the national prevalence and total numbers of
people age 71 and older, by age group, with any dementia and with AD or
vascular dementia in 2002. According to their calculations, 13.9
percent of Americans age 71 and older have some type of dementia, 9.7
percent of Americans in that age group have AD, and 2.4 percent have
vascular dementia. AD accounted for about 70 percent of all dementia
cases among people 71 and older. As in other studies, the ADAMS analysis showed that the prevalence
of dementia increases significantly with age. Five percent of people
ages 71 to 79, 24.2 percent of people 80 to 89, and 37.4 percent of
those 90 years or older were estimated to have some type of dementia.
The estimated rate of Alzheimer’s also rose greatly with older age—from
2.3 percent of people ages 71 to 79 to 18.1 percent of people 80 to 89
to 29.7 percent of those age 90 and older. The ADAMS investigators
found fewer years of education and the presence of at least one APOE e4
allele, a genetic risk factor for AD, to be strong predictors of AD and
other dementias. Richard Suzman, Ph.D., director of NIA’s Behavioral and Social
Research Program, which jointly directs the HRS, said the ADAMS data
will prove particularly valuable not only in assessing the prevalence
of dementia, but also its impact. “ADAMS, with its link to the data
about the health, economic, and family resources of individuals in the
study, will help us to characterize more fully the burden of dementia
on individuals, caregivers and the nation’s health care system,” he
says. The ADAMS report is the latest published study to estimate the
prevalence of dementia and AD among older Americans. “These assessments
have provided a range of estimates, based on differing methodologies
and approaches,” explains Dallas Anderson, Ph.D., program director for
population studies in NIA’s Dementias of Aging Branch. For example,
some studies have included lower age ranges than ADAMS or broader
characterizations of dementia, or have sampled participants in a
specific community as a base for national extrapolations. A study
reported in 1998 (Brookmeyer et al., 1998) combined incidence data from
four community-based studies, estimating that national Alzheimer’s
prevalence among individuals age 60 years or older would rise from 2.3
million in 1997 to 8.6 million in 2047. Widely cited estimates based on
the prevalence of Alzheimer’s disease in a Chicago-based community
(Hebert et al., 2003), and an earlier comparable study using data from
East Boston (Evans et al., 1990) forecast the number of those age 65 or
older with AD to be 5.1 million in 2010. Despite the varied approaches and findings, however, NIA experts
point out, the numbers of people with dementia, and Alzheimer’s
specifically, will certainly increase until ways to delay the
progression or prevent the dementia are found. Advancing age is the
most common known risk factor for Alzheimer’s disease. The HRS is an ongoing national survey of 22,000 adults age 51 and
older that began in 1992, providing data that helps researchers, policy
makers and others understand the life circumstances of older adults and
helps address the challenges of the nation’s rapidly aging population.
The ADAMS and HRS data are made publicly available to researchers
seeking to conduct studies about the older U.S. population. For further
information about the HRS and ADAMS, visit hrsonline.isr.umich.edu or www.nia.nih.gov/ResearchInformation/HRS.htm.
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Sources: National Insititute of Mental Health, See also blogposts in Psychiatric Disorders: General and Psychiatric Disorders: Aging
Dr. Jeffrey Speller
Dr. Tanya Korkosz
Psychopharmacology Associates of New England
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